Most book covers get judged at thumbnail size, in about a second. These are the mistakes we see most often: 1. Skipping the thumbnail test. Shrink your cover to stamp size. If you can’t read the title, it’s too small. 2. Ignoring genre signals. Readers browse by genre first. Stand out inside the conventions, not against them. 3. Weak type hierarchy. Title first, then author name, then tagline. If they compete, nothing gets read. 4. Designing for ebook only. Print needs CMYK, 300 dpi, bleed, and a spine sized to the page count. We’re British Book Publishing, a UK team offering book cover design, layout, and illustration for independent authors.